High polymers for forming an invisible, soil-resistant coating on canvas

ABSTRACT

Protection against soiling of textiles and of paintings produced on unsized canvas with a paint consisting of a pigment suspended in an organic solution of an acrylic resin is achieved by application thereto of a viscous solution of a water-soluble resin which forms a semi-impervious, transparent, flexible plastic coating on the surface which is invisible to the eye and which is easily removed from the canvas without affecting either the canvas or any painting or other decoration thereon.

United States Patent Brenner 1 1 Get. 1, 1974 [5 HIGH POLYMERS FORFORMING AN 2,986,471 5/1961 Rudd 117/6 x INVHSHBLE SOILSESTANT CQA'HNG()N 3,068,120 12/1962 Jacobson et al. l 17/ 139.5 C

CANVAS Inventor: Abner Brenner, 7204 Pomander Ln., Chevy Chase, Md.20015 Filed: Mar. 26, 1973 Appl. No.: 344,791

References Cited UNITED STATES PATENTS 7/1934 Serrington 117/166 4/1936Morrison 35/66 9/1943 Whitehead ll7/l66 X Primary ExaminerWilliam D.Martin- Assistant Examiner-Theodore G. Davis Attorney, Agent, orFirm-Lawrence I. Field ABST CT Protection against soiling of textilesand of paintings produced on unsized canvas with a paint consisting of apigment suspended in an organic solution of an acrylic resin is achievedby application thereto of a viscous solution of a water-soluble resinwhich forms a semi-impervious, transparent, flexible plastic coating onthe surface which is invisible to the eye and which is easily removedfrom the canvas without affecting either the canvas or any painting orother decoration f thereon.

l2 Claiins, N0 Drawings HIGH POLYMERS FOR FORMING AN ENVESEBLE,SOIL-RESISTANT COATING ON CANVAS This invention relates to theprotection of paintings and textiles from soiling. More particularly itrelates to the provisions of a relatively impervious, transparentflexible plastic coatings on canvas, which are invisible to the eye andwhich are easily removed from the canvas without affecting either thecanvas or any painting or other decoration thereon.

Numerous incidents have been reported in the press of persons defacingpaintings hanging in public galleries or in museums, wherein markingswere made on the surface of the paintings, usually with crayons, aerosolsprays or other marking tools. The removal of such markings withoutdamage to the art work is often difficult and time consuming.

Hence it will be evident that a need exists for a semiimpervious,invisible, flexible coating to protect artists paintings from soiling ordefacement. The present invention is directed to the protection of aspecific type of artists painting, namely paintings produced on urisizedcanvas with a paint consisting of a pigment suspended in an organicsolution of an acrylic resin.

Paintings of this type were first produced about three decades ago.Because the canvas wasunsized, the paint soaked into it. The texture ofthe canvas was retained and the cloth had the appearance of having beendyed. This art work was esthetically pleasing because it did not havethe high gloss and annoying reflectivity characteristic of conventionaloil paintings produced on sized canvas with pigments suspended inlinseed or similar oil. However, the very characteristic that isresponsible for the pleasing effect is the source of a difficulty, asthe painting exhibits virtually the same absorptivity and capillarity asthe original canvas. Consequently, the paintings are easily soiled andare difficult to restore. The difficulty is even greater in the case ofsome paintings which had areas of unsized, unpainted canvas.

In contrast to the above type of painting, conventional oil paintings,which are produced on sized canvas with an oil that in time polymerizesand oxidizes, have a nonporous, impervious surface, which if soiled canbe cleansed with water and a detergent. The surface of oil paintings canbe protected by applying an alcoholic solution of certain resins, whichwhen soiled or deteriorated can be dissolved off and reapplied as isalready known.

At the present time no process or treatment appears to be known forproducing protective coatings on unsized canvas, which would beimpervious, invisible, and flexible; and, hence which could be appliedto the new type of paintings without changing their appearance. Theprincipal object of this invention is to provide a protective coatingwhich would resist soiling from moist or greasy contacts, settling ofdust or airborn contaminants, and damage by minor accidents orvandalism, such as pencil or crayon marks andwhich is capable of beingeasily removed with its contaminant and thus to permit a new coating tobe applied.

This and other objects will become apparent or will be pointed out inthe description which follows.

The protective coating capable of achieving the stated objective whenapplied to canvas should have the following characteristics:

1. It should be sufficiently impervious so as to prevent for about Iminute the penetration of common liquids, like perspiration. moisture.liquor and oils. The expression semi-impervious in this specificationmeans that the treated canvas prevents the passage of a drop of mineraloil (SAE No. 20) for a minute or more. In comparison, a drop of such oilplaced on untreated canvas is adsorbed immediately.

2. It should be readily dissolved off without detriment to the paintedsurface and easily reapplied.

3. It should be virtually invisible, so as not to alter the appearanceof the unpainted canvas or of the painting itself; for example, itshould have no detectable gloss when viewed at a reasonably direct angleand should not be detectable at a viewing distance of about 3 or 4 feet.

4. It should be flexible. This property is necessary because thepainting should be capable of being made into a roll for ease oftransportation without the coating cracking.

5. The solution of the protective coating should be easy to apply. Thisrequires that it be of a viscosity which permits the application of athick layer without running and yet exhibits sufficient fluidity tolevel out before drying.

Conventional lacquers applied to the surface of canvas with a brush didnot produce an impervious surface coating. Even successive applicationsof a lacquer did not make canvas proof against soiling. Consequently anevaluation of water soluble resins was undertaken.

The following procedure was used. The aqueous high polymer solution(which usually was quite viscous) was applied to a weighed specimen ofcanvas with an ordinary paint brush and the specimen allowed to dryovernight. The increase in weight was noted.

A series of soiling agents was then applied to the treated canvas,allowed to remain for about two minutes, and the excess wiped off. Thesoiled specimen was allowed to dry. The removal of the soil along withthe resin was accomplished by alternately wetting and lightly spongingthe surface of the canvas at intervals followed by occasional rinsingunder a gentle stream of water. This cleansing process required aboutfive minutes.

The soils applied to the coated canvas were of three different types:(a) commercial lndia inks of five different colors including black,which was probably an aqueous suspension of carbon; (b) marks made withan ordinary lead pencil and with a china-marking pencil, which left awaxy trace; (c) a suspension of raw umber in oil prepared according to aUS. Federal Specification No. "IT-P-30b, Sept. 10, 1959. The suspensionconsisted of raw umber, 35 g; white petrolatum, 6 g; and mineralspirits, 40 g. This umber-soil was the most difficult to remove of thethree. In those instances in which the raw umber penetrated into theinterstices of the canvas, it could not be removed, even by intensivelaundering with soap and water.

To confer protective action to canvas, it was found that the resins hadto be applied in strong solutions of 8 percent to 15 percent by weight.Solutions below 8 percent by weight conferred inadequate protection. Themore concentrated solutions of the resins were viscous, having aconsistency like a table syrup or glycer- The canvas used in theseevaluations had a weight of about 40 to mg per square cm. From thethickness of the canvas (about 0.75 mm) and this weight, it iscalculated that the canvas was about 40 to 50 percent voids. The weightof resin which had to be present on one side of the canvas to protect itranged between 4 and mg per cm This amount would be sufficient to fillonly a fraction of the voids in the canvas.

While not wishing to be bound by any specific theory as to why certainwater soluble resins are more effective than others, it appears thattheir effectiveness may be due to the formation of a semi-imperviouscoating on the surface of the canvas and not on the filling up of theinterstices.

The water soluble resins which were found to impart some protectiveaction against soiling of canvas included the following: ordinary glueor gelatin, polyvinyl alcohol, acrylic acid polymers, a number ofcellulose derivatives, and natural gums. Of those, sodiumcarboxymethylcellulose in a 12 to 15 percent solution gave the bestresults. The effectiveness of sodium carboxymethylcellulose inprotecting canvas against soiling should not be confused with itsutilization in detergents, where it is used in low concentrations of 0.1percent or less to prevent soil from resettling on fabrics duringlaundering. In protecting canvas, sodium carboxymethylcellulose(hereinafter designated as CMC) does not appear to function as adetergent as evidenced by the following experiment. Canvas (without anyprior treatment) was soiled with the materials mentioned previously. Thecanvas was then heavily treated with CMC which was subsequently removedwith water. The soils were not removed by this procedure, which,however, would have been the case if the protective action of CMC weredue to detergency.

Furthermore, the action of CMC in protecting canvas does not appear torequire the use of it in conjunction with wetting agents, as has beensuggested in U.S. Pat. No. 2,986,471 which issued May 30, I961 on thetreatment of impervious surfaces such as automobile bodies. In such ause, the wetting agent apparently assists removal of soil from anonporous body through a lowering of the surface tension. However, inthe application of CMC to canvas, the incorporation of wetting agentswas found to be detrimental to the formation of the impervious film thatserves as a barrier to soils.

As indicated above, in order to impart an appreciable resistance tosoiling, canvas should be coated with sufficient CMC solution to provide4 to 10 mg per cm of the resin on one side and double this amount ifboth sides of the canvas are treated.

Neither bare canvas nor unsized, painted canvas (painted with acrylicresins dissolved in organic solvents) exhibit any appreciable change inappearance or color when treated with these amounts of CMC. Furthermore,the treated surface does not have any appreciable gloss. Only byexamining the surface at a glancing angle can the presence of a slightgloss be detected.

CMC is commercially available in a number of grades, the main differencebeing the viscosity of the solutions. For the purpose of protectingcanvas from soiling, it is desirable to obtain the highest concentrationof CMC in a solution of lowest viscosity in order that it can be readilypainted onto a surface. A particularly preferred grade of CMC for thepresent invention was found to be CMC-7L1 manufactured by HerculesIncorporated.

The viscosity of the 10 percent solution of this grade of CMC rangedbetween 4,000 and 7,000 centipoises.

The viscosity of the 12 percent solution, which is the concentrationfound most suitable for treating canvas, ranged between 13,000 and38,000 centipoises. The viscosity was like that of glycerine or a tablesyrup and no difficulty was experienced in painting this solution on acanvas surface. The viscosity of the 15 percent solution ranged between90,000 and 180,000 centipoises, and this solution was found to be tooviscous to apply readily. On a small scale the solution was preparedwith stirring and the slow addition of CMC. Too vigorous stirringcreated a foam which was difficult to dissipate. Another procedure foundsuitable was to add the CMC in small increments to a container of waterfollowed by stoppering and shaking vigorously by hand. There wasformation of some lumps, but by shaking the container a few times eachday over a period of a few days, these broke up and dissolved.

The solution of CMC is improved by some additives. The solution isattacked by mold and putrifies in several weeks. The addition of variousstabilizers is often desirable as is known in the art. For example, theaddition of phenol, about 0.5g per liter, to the CMC solution was foundto prevent the putrification.

Another useful additive to the CMC solution is an optical brightener forthe purpose of whitening the canvas, which usually has a yellowish castthat is slightly intensified by the CMC film. The optical brightenerabsorbs ultraviolet light and converts it into visible blue light whichserves to neutralize the yellow tint of the canvas. One opticalbrightener that I have found suitable is TINOPAL 4MB/ 154, product ofthe Geigy Chemical Corporation. Since the brightener is only sparinglysoluble in cold water, it should be dissolved in a small quantity of hotwater and added to the main quantity of cold water just prior to addingthe CMC. In the presence of the CMC the brightener did not precipitateout. The optical brightener is used in the CMC solution at aconcentration of about 0.25g per liter. The optical brightener improvedthe whiteness of the canvas when viewed under daylight or fluorescentlighting, but there was no appreciable whitening effect underincandescent lighting. The brightener very slightly altered the color ofthe painted areas. This could be detected only by a side by sidecomparison.

Some variations of the CMC treatment were investigated. Lowering the pHof the solution to 3.5, which meant that the CMC was present as the acidinstead of the sodium salt, did not affect the protective value of thefilm. The incorporation of glycerine in the solution to the extent of 15percent of the weight of the CMC had no apparent effect on theprotective value of the film. Glycerin would probably make the film moreflexible. Treatment of a CMC film on canvas with a 10 percent solutionof alum converted the CMC into a brittle, insoluble film. When thisspecimen of treated canvas was soiled as previously described, the soilscould not be removed with water. This confirms the importance of thesolubility of the CMC film for the cleaning process. In another variantof the application of CMC, a 5 percent solution was applied two or threetimes with drying in between each application. This process did notresult in any improvement in protective action and the appearance of thecanvas was less satisfactory than with one application of a 12 percentsolution.

Canvas treated with CMC retains some flexibility. It can be slowlyrolled around a cylinder 2 inches in diameter without cracking. Asmaller radius of curvature causes cracking of the coating, which can bedetected by moistening the surface with a mineral oil containing anoil-soluble dye. The flexibility of treated canvas is important, becauseon occasion a painting may need to be rolled for transportation.

The canvas used in the practices of this invention, when wetted, shrankabout 0.5 percent. In contrast, the same canvas treated with CMC shrankabout 3 percent. A strip of canvas, after treatment with CMC solution,was prevented from shrinking by application of a spring tension. Theforce amounted to a few pounds per linear inch of width of strip.However, there is no shrinkage of canvas if it is rigidly mounted in aframe prior to treatment with CMC solution and allowed to dry in theframe. I have found that canvas so treated and then cut out of the frameexhibited no appreciable shrinkage (less than 0.1 percent).

The shrinkage of canvas treated with CMC, or the tension generated ifthe shrinkage is prevented, requires some precautions in applying theCMC treatment to paintings if the frames are to be prevented fromsubsequently warping. The frame of the painting should be made rigid,for example by securing it with C-clamps to a table top or to a sheet ofinch-thick plywood. A large painting may require clamping to a wall orfloor. The CMC solution is then applied liberally with a good qualitypaint brush of as large a size as practicable (4 or 6 inch width), andthe entire painting should be coated before any portion of the coatingdries. It is helpful to view the moist surface at an angle to detect anyareas that may have been missed. After the CMC has dried, the frame ofthe painting can be released from the clamps. The frame will be found tostill be true and the painting taut as if recently stretched.

A painting need not be tightly stretched in its frame before treatingwith CMC solution, since it is found that slack areas as well as ripplesdisappear as the CMC solution dries. It is possible that the gradualdrying of the CMC solution provides a more uniform distribution ofstresses than that obtained in stretching a painting manually.

In this connection, paintings treated with CMC showed an unexpectedbenefit, in that they were not sensitive to changes in humidity andtemperature, but maintained their tautness winter and summer. Incontrast, untreated paintings on unsized canvas (painted with acrylicresins in organic solution) often developed large, unsightly ripples incold dry weather owing to the expansion of the canvas. In hot humidweather the canvas shrinks and the ripples disappear. If the paintingsare tightened in winter, then during the humid period it is possiblethat the canvas would be put under an undue strain. A painting, whichhad been treated with CMC, during an extensive test period did notundergo these cycles of slackness and tautness, but maintained a smooth.taut appearance and without warping the frame.

in treating paintings with CMC in accordance with my invention thefollowing should be noted:

a. Only paintings on a frame should be treated. lf paintings are treatedin the unmounted condition, the painting may not be capable of beingsubsequently stretched on a frame to yield a plane, taut surface,because the CMC coating makes the canvas less yielding.

b. If the CMC solution is also applied to the back of the painting, careshould be taken to prevent the solution from oozing between the canvasand the wooden frame. If this is not done it is possible that afterdrying the canvas will be found to be glued to the frame and a line orcrease may form in the canvas on the viewing side along the edge of theframe. One way to avoid this difficulty is to insert a strip ofpolyethylene between the frame and the canvas. The polyethylene strip isthen removed after the CMC dries.

It should be noted that the 12 percent CMC treatment is applicablespecifically to paintings produced with an acrylic resin dissolved in anorganic solvent, which paintings have an absorptiveness somewhat akin tothat of the unprimed, bare canvas. The application of the CMC treatmentto paintings produced with the water-emulsion type of acrylic paintrequires a slight modification in the procedure. This is because theemulsion is broken on the surface of the treated canvas, and, hence, theresin does not sink into the canvas as in the case of the organic typeof acrylic solution. Consequently, the former type of paint yields amore impervious surface than the latter, but by the same token theformer does not produce the pleasing, dyed or stained appearance of thelatter. Because of the smaller absorptiveness of the emulsion type ofpainted surface, the liberal application of a thick layer of CMCsolution may result in the production of glossy patches on the painting.To prevent this, either the CMC solution should be brushed on morethinly or a more dilute solution should be used, for example 8 or 10percent, or a 12 percent solution of a related cellulose derivativehydroxypropylcellulose may be used. Although not as protective as CMCwhen applied over bare canvas, it provides satisfactory protection whenapplied over the emulsion type of painted surface. It has the advantageover CMC of forming a more flexible film and solutions of a givenconcentration have a lower viscosity than CMC solutions.

Although sodium carboxymethylcellulose (CMC) is the particularlypreferred water-soluble resin for protecting the unprimed paintings,several other resins were found to be almost as good and still othershad some protective action. However, protective action was not the solecriterion in establishing that a resin was satisfactory, as color,transparency, and flexibility were also important and a resin could beconsidered unsatisfactory on the basis of any of these properties.

For example, ordinary gelatin had good protective value, but the filmswere too brittle in the thickness required for protection.

Methylcellulose in concentrations of 10 to 20 percent yielded almost asgood protection as CMC. The film had the advantage of being moreflexible than CMC, but was slightly more yellowish in color. Removal ofthe raw umber soil from treated canvas was not quite as rapid orcomplete as with CMC.

Hydroxypropyl cellulose applied as a 15 percent solution, was not asprotective as either CMC or methylcellulose.

Hydroxyethyl cellulose in 15 percent solution gave protection aboutequal to that provided by hydroxypropyl cellulose but had no advantagesthereover.

Several noncellulosic water-soluble resins also yielded some protectionto canvas, although not as much as the cellulose compounds alreadydiscussed. Polyvinyl alcohol (a low viscosity grade was used) in 10 to15 percent solutions were moderately protective. India ink marks werenot as completely removed as with the films of cellulosic derivatives. Adisadvantage of polyvinyl alcohol was that to prepare the solution thecompound had to be dissolved in nearly boiling water and similarly, thesoiled films on canvas required hot water for most efficient removal.

Finally, for comparison with CMC, canvas was primed with gesso, (whichconsists of whiting dispersed in an organic solution of a resin) andthen treated with various soils. The raw umber soil was fairlycompletely removed with soap and water, but the laundering did notsuffice to remove the various India inks as completely as did rinsing ofCMC coatings with water.

These results suggest that for priming canvas prior to painting artistsmight consider the use of aqueous solutions of CMC, or polyvinylalcohol, or some of the other water-soluble resins, as alternatives tothe timehonored materials glue or gesso. lf it is necessary to renderthe coating unattackable by water, polyvinyl alcohol can beinsolubilized by treatment with a solution of formaldehyde and CMC witha solution of alum.

. It was originally assumed that the protection of canvas from soilingwould require the filling up of the interstices by a resin. However,after some protective procedures were developed it appears that theprotection of the canvas resulted from the presence of a semiimperviousfilm on the surface and not from the filling up of the interstices.

The semi-impervious nature of the protective film that is formed bysolutions of CMC and the other protective resins is easily demonstratedby placing a drop of mineral oil containing an oil-soluble dye on thesurface of the treated canvas. The drop is allowed to remain for aboutone minute and then wiped off. The dye will be found either not to havepenetrated at all or at most only through a few pinholes. Thepenetration of mineral oil without any added dye can be readily detectedby holding the specimen up to the light and noting the translucentareas. In contrast to the behavior of the protective resins, mineral oilplaced on canvas treated with a conventional lacquer penetratescompletely through the cloth within a few seconds.

. demonstrated by immersing the end of a strip of treated canvas in theoil dye solution. The latter will be found to have risen up into theinterior of the strip, but without having penetrated to either surface.

To a first approximation, the protective value of the various surfacefilms that were applied to canvas correspond with the observedresistance to the penetration of mineral oil through the canvas. Oneexception was the coating of polyvinyl alcohol. It was about asresistant to penetration as CMC films, but it did not give the degree ofprotection against India inks that would have been expected on the basisof the good showing in the test.

it has been found that penetration of the resin solution into the canvasis not required for establishing protection against soiling. A highviscosity type of CMC, which formed a gel at a concentration of percent,was plastered on canvas with a spatula and allowed to dry. The treatedcanvas had good resistance to soiling. A similar result was obtainedwith a l0 percent gel of agar-agar.

The protective action of CMC and other watersoluble resins is thuspartially due to the existence of a relatively impervious film on thesurface of the canvas.

It appears that two factors are mainly responsible for the formation ofthe protective surface coating namely: 1. restricted penetration of thesolution into the canvas, and

2. formation of a gel, which has some tensile strength, early in thedrying process.

Penetration of the solution into canvas is restricted by two propertiesof the solution, i.e., by the viscosity and the surface tension of thesolution. The role of viscosity is illustrated by the behavior of a 10percent solution of polyvinylpyrrolidone (PVP). The solution has a lowviscosity compared to a solution of CMC and readily penetrates into thecanvas, but it does not confer any protective action. By adding to thePVP solution only 2 percent of a grade of CMC that has the property ofgreatly increasing the viscosity of the solution, an appreciableprotective effect was obtained, although the 2 percent addition of CMC,used by itself, conferred negligible protection. A similar result wasobtained with the polyethylene oxide resin, which has no protectivevalue by itself, and with a 2 percent addition of CMC. v

The surface tension of the solution prevents rapid penetration into theinterstices of the canvas. This is because the presence of the trappedair in the fibers prevents a rapid wetting of the canvas. The lowsurface tension of organic solutions of resins compared to aqueoussolutions may be one of the reasons that these solutions do not formprotective surface films. When a wetting agent was added to a solutionof CMC, the protective action of the resulting film on canvas wassignificantly inferior to that of the CMC solution without the wettingagent.

It is also possible the water-soluble resins form a portective barrierlayer more readily than solutions of conventional lacquers because thewater solution quickly turns into a gel after it becomes slightlyconcentrated by evaporation of a small percentage of water. The gel thusformed has a certain tensile strength and holds together as a film as itdries instead of slowly being absorbed into the interstices of thecanvas, as would be the case for a nongelling solution.

Whatever the fine reasons for its effectiveness it is evident that theprotective coating can prevent soiling simply by acting as a barrierlayer. Another important protective feature of the surface layer is itscapacity to swell when wet with water. This would slow penetration ofaqueous soils into the interior of the canvas. It is also likely thatthe swelling of the film closes up the pinholes. The swelling of the CMCfilms may be the reason that they are more effective in preventingsoiling by India inks (which are aqueous solutions) than by the rawumber-soil. Also, this is consistent with the observed better protectionof CMC films against inks in comparison with polyvinyl alcohol films. Athird characteristic of the resins is their ready removal with wateralong with the adsorbed soil.

It will be noted that the protection of conventional oil paintings wasnot evaluated because the surface of these are impervious and, at leasttheoretically, could be cleansed with water and a detergent.

Having now described preferred embodiment of the present invention, itis not intended that it be limited except as may be required by theappended claims.

What is claimed is:

l. A process for imparting a semi-impervious, invisible, flexible,protective, soil-resistant surface to canvas and to surfaces of unsizedcanvas painted with artist's acrylic-type of paint consisting of acrylicresin in organic solvent along with pigment which comprises applying tothe surface of said canvas a viscous solution of water-soluble resins ata concentration of 8 percent to 20 percent by weight and permitting saidsolution to dry.

2. The process of claim 1 wherein the solution is applied by brushing.

3. The process of claim 1 wherein a soil resistant surface, such thatthe surface is not penetrated in one minute by an aqueous dye solutionor by mineral oil, is produced on said canvasv 4. A process as set forthin claim 1 including in addition washing the surface with water so as toredissolve the resin which carries along with it soils present on saidsurface.

5. The process of claim 1 wherein the viscous solution is an 8 percentto percent aqueous solution of sodium carboxymethyl-cellulose, having aviscosity of 5,000 to 40,000 centipoises.

6. The process of claim 5 including the addition of phenol at aconcentration of 0.5 g/l to the solution of sodiumcarboxymethylcellulose for the purpose of preventing the growth of moldon long time storage or the solution.

7. The process of claim 1 wherein the viscous solution contains 0.05 gto 0.5g of an optical brightener with a blue fluorescense per liter ofthe solution for the purpose of neutralizing the yellowish tint of thetreated canvas and for making the latter appear whiter under daylight orunder fluorescent illumination.

8. The process of claim 1 wherein the viscous solution is an 8 to 15percent solution of hydroxyethylcellulose.

9. The process of claim 1 wherein the viscous solution is an 8 to 15percent solution of hydroxypropyl cellulose.

10. The process of claim 1 wherein the viscous solution is a 10 percentto 20 percent aqueous solution of methylcellulose.

11. The process of claim 1 wherein the viscous solution is a watersolution of a water-soluble cellulose derivative selected from the groupconsisting of hydroxy alkyl celluloses, carboxy alkyl celluloses, alkylcelluloses and alkali metal salts of said alkyl or substituted alkylcelluloses.

12. The process of claim 1 wherein the viscous solution is a 10 to 20percent solution of polyvinyl alcohol in water.

1. A PROCESS FOR IMPARTING A SEMI-IMPERVOUS INVISIBLE, FLEXIBLE,PROTECTIVE, SOIL-RESISTANT SURFACE TO CANVAS AND TO SURFACES OF UNSIZEDCANVAS PAINTED WITH ARTIST''S ACRYLIC-TYPE OF PAINT CONSISTING OFACRYLIC RESIN IN ORGANIC SOLVENT ALONG WITH PIGMENT WHICH COMPRISESAPPLYING TO THE SURFACE OF SAID CANVAS A VISCOUS SOLUTION OFWATER-SOLUBLE RESIN AT A CONCENTRATION OF 8 PERCENT TO 20 PERCENT BYWEIGHT AND PERMITTING SAID SOLUTION TO DRY.
 2. The process of claim 1wherein the solution is applied by brushing.
 3. The process of claim 1wherein a soil resistant surface, such that the surface is notpenetrated in one minute by an aqueous dye solution or by mineral oil,is produced on said canvas.
 4. A process as set forth in claim 1including in addition washing the surface with water so as to redissolvethe resin which carries along with it soils present on said surface. 5.The process of claim 1 wherein the viscous solution is an 8 percent to15 percent aqueous solution of sodium carboxymethyl-cellulose, having aviscosity of 5,000 to 40,000 centipoises.
 6. The process of claim 5including the addition of phenol at a concentration of 0.5 g/l to thesolution of sodium carboxymethylcellulose for the purpose of preventingthe growth of mold on long time storage or the solution.
 7. The processof claim 1 wherein the viscous solution contains 0.05g to 0.5g of anoptical brightener with a blue fluorescense per liter of the solutionfor the purpose of neutralizing the yellowish tint of the treated canvasand for making the latter appear whiter under daylight or underfluorescent illumination.
 8. The process of claim 1 wherein the viscoussolution is an 8 to 15 percent solution of hydroxyethylcellulose.
 9. Theprocess of claim 1 wherein the viscous solution is an 8 to 15 percentsolution of hydroxypropyl cellulose.
 10. The process of claim 1 whereinthe viscous solution is a 10 percent to 20 percent aqueous solution ofmethylcellulose.
 11. The process of claim 1 wherein the viscous solutionis a water solution of a water-soluble cellulose derivative selectedfrom the group consisting of hydroxy alkyl celluloses, carboxy alkylcelluloses, alkyl celluloses and alkali metal salts of said alkyl orsubstituted alkyl celluloses.
 12. The process of claim 1 wherein theviscous solution is a 10 to 20 percent solution of polyvinyl alcohol inwater.